Due to their advantages such as light weight, low power consumption, low irradiation and capability of saving space significantly, liquid crystal displays have replaced traditional cathode ray tube displays and are widely applied in various display fields such as home, public space, office locations and personal electronic products.
As illustrated in FIG. 1, a known liquid crystal display comprises display pixels (units) and thin film transistors (TFTs) for controlling display data loading, wherein the thin film transistor is generally of a bottom gate structure (gate of the thin film transistor under the semiconductor layer) comprising: a substrate 1, on which a gate metal layer 2, a gate insulating layer 3, a semiconductor layer 4 and a source-drain electrode layer 5 are disposed in this order from bottom to top; a display pixel comprises a common electrode 6, a passivation layer 8, a pixel electrode 7 and liquid crystal (on the pixel electrode 7, not shown in drawings) disposed on the passivation layer 8. The pixel electrode 7 is connected to a drain of the thin film transistor, the common electrode 6 is connected to the common electrode line 9, the pixel electrode 7 loads display data through the TFT, a driving electric field is generated between the common electrode 6 and the pixel electrode 7 and liquid crystal molecules rotate under the action of this driving electric field to display images.
With the TFT of bottom gate structure, the gate metal layer 2 blocks light emitted from the backlight source on the array substrate side, while exterior light (entering from the color filter substrate side) is blocked by the black matrix BM. The inventor found out however, when the color filter substrate and the array substrate are in misalignment, or when there is any failures in process of manufacturing the array substrate, the semiconductor layer tends to be exposed. Then TFTs' leakage current increase abnormally due to the irradiation of exterior light. As a result, the liquid crystal display encounters display defectiveness such as becoming greenish and non-uniform gray scale (X-talk).
In addition, for liquid crystal displays, particularly high resolution products, it is required to reduce resistance of common electrode, otherwise delay occurs due to the too big resistance of common electrode, and display defectiveness such as becoming greenish and non-uniform gray scale (X-talk) are likely to occur, thereby influencing the picture quality. However, if the line width of common electrode is increased to reduce resistance of common electrode, the aperture ratio will become smaller.